Hurricane Ernesto Discussion Number  21
NWS National Hurricane Center Miami FL       AL052024
500 PM AST Fri Aug 16 2024

After looking quite ragged this morning, Ernesto's structure on
satellite has made a comeback.  A burst of convection that began
after the last advisory has wrapped around the western side of the
hurricane, and the eye has also tried to clear. The structural
improvement in Ernesto was also seen from the last couple of Air
Force and NOAA Hurricane Hunter fixes which indicated the eyewall
definition had improved while remaining quite large. This improved
eyewall can also be seen on radar imagery out of Bermuda. Before
departing, the peak flight-level winds from the NOAA-P3 aircraft was
107 kt at 750 mb, while the Air Force reconnaissance measured 99 kt
at 700 mb. While the satellite-based intensity estimates are a bit
lower, the initial intensity will be held at 85 kt given the higher
aircraft observations and improvement in structure this afternoon.
Of note, Saildrone SD-1068 appears to currently be in the northwest
eyewall of Ernesto and recently reported wind gusts of
hurricane-force and significant wave heights up to 36 feet.

Ernesto has maintained a north-northeast track this afternoon,
estimated at 035/11 kt. There isn't much change in the track
thinking this afternoon, as a mid to upper-level trough that has
been helping the hurricane move poleward will leave Ernesto behind
over the next day or two. While Ernesto will remain steered by a
subtropical ridge to its southeast, it is still forecast to
temporarily slow its north-northeastward motion. Thereafter, another
shortwave trough moving into the Great Lakes region is expected to
dig southeastward over the Eastern U.S. and act as a kicker that
will help to accelerate Ernesto more northeastward between forecast
days 2 to 3. There is not much change to the track guidance this
afternoon, just perhaps a touch slower after the next 24 hours, and
the NHC track forecast lies very close to the prior one, close to
the multi-model consensus aids. Based on the latest track, Ernesto's
large eye will likely be very near or over Bermuda tomorrow
morning.

Intensity-wise, the model guidance continues to be insistent that
Ernesto will weaken some in the short term as it battles 20-25 kt
vertical wind shear out of the west, though so far Ernesto has been
been more resilient than expected, possibly due to its large size.
Nonetheless, this NHC intensity forecast will show some weakening,
though not as much as IVCN or some of the hurricane-regional models
over the next 24 h. After that time, shear decreases again while
Ernesto will remain over 27-28 C sea-surface temperatures, and the
intensity guidance responds to these more favorable conditions by
showing some restrengthening. Finally, after 60 h, Ernesto will
quickly cross the north wall of the Gulf Stream as the shear also
begins to rapidly increase again. The NHC intensity forecast shows
the hurricane completing extratropical tradition just after 72 h as
the system passes nearby the southeastern coast of Newfoundland
Canada.

Key Messages:

1. Ernesto is expected to bring a prolonged period of strong winds
and storm surge on Bermuda that is beginning currently and expected
to continue through Saturday night. A hurricane warning is in effect
for the island, and preparations to protect life and property should
be completed as tropical-storm-force winds are already
being observed on the island.

2. Heavy rainfall associated with Ernesto is expected to impact
Bermuda through Saturday and will likely result in considerable
life-threatening flash flooding, especially in low-lying areas on
the island.

3. Even though Ernesto is forecast to remain well offshore the U.S.
East Coast, swells generated by the hurricane are expected to affect
the area through the weekend.  Beach goers should be aware of a
significant risk of life-threatening surf and rip currents, and stay
out of the water if advised by lifeguards.  Surf and rip currents
are also possible on the Turks and Caicos, the Bahamas, Bermuda,
and Atlantic Canada during the next few days.


FORECAST POSITIONS AND MAX WINDS

INIT  16/2100Z 30.6N  65.6W   85 KT 100 MPH
12H  17/0600Z 31.9N  65.1W   80 KT  90 MPH
24H  17/1800Z 33.1N  64.5W   75 KT  85 MPH
36H  18/0600Z 34.6N  64.0W   70 KT  80 MPH
48H  18/1800Z 36.6N  63.0W   75 KT  85 MPH
60H  19/0600Z 39.8N  61.0W   80 KT  90 MPH
72H  19/1800Z 43.5N  57.0W   70 KT  80 MPH
96H  20/1800Z 50.0N  42.5W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  21/1800Z 53.5N  22.4W   35 KT  40 MPH...POST-TROP/EXTRATROP

$$
Forecaster Papin